Numerous industrial processes discharge streams which contain a mixture of various gaseous fluids. There is increasing concern that some of the constituents of the effluent streams may cause significant environmental problems, and that these streams therefore should not be released into the atmosphere. Carbon dioxide is a compound which is a constituent of many of the effluent streams released from industrial processes and whose release into the atmosphere is causing increasing concern.
It is hypothesized that carbon dioxide released into the atmosphere acts as a green-house gas and that too high a concentration of green-house gases in the atmosphere will cause global warming. In response to this potential threat, many governmental bodies have either enacted or plan to enact regulations limiting the quantity of carbon dioxide which can be released into the atmosphere. These regulations can hamper many industries because the combustion of virtually any hydrocarbon fuel with air produces an effluent containing carbon dioxide, nitrogen, and gaseous combustion products.
The mixture of gases which results from the combustion of a hydrocarbon with oxygen or air is hereinafter referred to as "flue gas." The chemical composition of flue gas depends on many variables, including but not limited to, the combusted hydrocarbon, the combustion process oxygen-to-fuel ratio, and the combustion temperature. In addition to carbon dioxide and nitrogen, flue gas may contain compounds such as, carbon monoxide, oxides of sulfur, oxides of nitrogen, and other constituents. The release of these compounds to the atmosphere also is coming under increasing public scrutiny and is the subject of increasing governmental regulation.
There are several types of commercially available systems which may be used for removing carbon dioxide from gas streams. One of the most commonly-used systems utilizes a selective amine absorption solution to strip the carbon dioxide from the gas stream. Unfortunately, this type of system will not tolerate high levels of particulates or oxides of sulfur. Particulates cause plugging, contamination, and erosion or corrosion of the treating process, while oxides of sulfur, such as sulfur dioxide (SO.sub.2), react irreversibly with the amine solution utilized in the system to form non-regenerable by-products. Therefore, if particulates or oxides of sulfur are present, extra process steps are required to remove the oxides of sulfur and particulates prior to stripping the carbon dioxide from a gas stream. These extra process steps add complexity and cost to the system.
In addition to being a hydrocarbon combustion product, carbon dioxide can be produced by natural processes and released to the environment during a non-combustion process. For example, carbon dioxide is produced by the thermal and biogenic processes which are believed to form hydrocarbons such as oil, natural gas, or coal. Carbon dioxide often is recovered with these hydrocarbons and released to the atmosphere by various post-production steps.
The increasing concern over the atmospheric release of carbon dioxide and other compounds demands methods by which to dispose of the deleterious compounds. Preferably, the methods should be capable of disposing of both carbon dioxide and other contaminants together, without the need to use a process step to dispose of carbon dioxide and another separate process step to dispose of other contaminants, such as oxides of sulfur and oxides of nitrogen.
As used herein, the following terms shall have the following meanings:
(a) "cleats" or "cleat system" is the natural system of fractures within a solid carbonaceous subterranean formation; PA1 (b) a "coalbed" comprises one or more coal seams in fluid communication with each other; PA1 (c) "formation parting pressure" and "parting pressure" mean the pressure needed to open a formation and propagate an induced fracture through the formation; PA1 (d) "reservoir pressure" means the pressure of a formation near a well during shut-in of that well. The reservoir pressure can vary throughout the formation. Also, the reservoir pressure of the formation may change over time as gaseous fluid is injected into the formation and fluids are produced from the formation; PA1 (e) "solid carbonaceous subterranean formation" refers to any substantially solid carbonaceous, methane-containing material located below the surface of the earth. It is believed that these methane-containing materials are produced by the thermal and biogenic degradation of organic matter. Solid carbonaceous subterranean formations include but are not limited to coalbeds and other carbonaceous formations such as antrium, carbonaceous, and devonian shales. The formations utilized by the invention include formations which are depleted of recoverable methane; PA1 (f) "preferentially sorbing", "preferentially sorbs", and "preferential sorption" refer to processes which occur within a solid carbonaceous subterranean formation that alter the relative proportions of the components of a gaseous fluid. These processes may alter the relative proportions of the components of a gaseous fluid by equilibrium separation, kinetic separation, steric separation, and/or any other physical or chemical processes or combination of processes which within a solid carbonaceous subterranean formation will selectively alter the relative proportions of the components of a mixture of gaseous fluids. Within the formation, the gases sorbed to the carbonaceous material of the formation will be enriched in relatively stronger adsorbing fluid components; PA1 (g) "sorption" refers to a process by which a gas is held by a carbonaceous material, such as coal, which contains micropores. The gas is held on the carbonaceous material in a condensed or liquid-like phase within the micropores, or the gas may be chemically bound to the carbonaceous material. PA1 (h) "flue gas" refers to the gaseous fluid mixture which results from the combustion of a hydrocarbon with oxygen or air. The composition of flue gas depends on many variables, including but not limited to, the combusted hydrocarbon, the combustion process oxygen-to-fuel ratio, and the combustion temperature. PA1 a) introducing a gaseous fluid, comprising the unwanted gaseous fluid component, into the formation to sorb the unwanted gaseous fluid component to the formation; and PA1 b) maintaining disposal conditions within the formation to ensure that at least 10 percent of a disposal saturation level of an unwanted gaseous fluid component remains sorbed to the formation. PA1 a) introducing a gaseous fluid, containing the unwanted gaseous fluid component, into the coal seam; and PA1 b) ceasing to introduce the gaseous fluid into the coal seam when the coal seam becomes saturated to a desired degree with the unwanted gaseous fluid component.